1) Field of the Invention
The present invention relates to rotational spindles and, more particularly, to an apparatus and method for testing spindles.
2) Description of Related Art
Spindles are used in a wide variety of machines to provide a mechanism for generating and/or transferring rotational motion. One typical spindle includes an electric motor coupled to a shaft. The motor and shaft are mounted in a housing and at least one end of the shaft extends from the housing to connect to a tool. Bearings, bushings, and spacers can be used to maintain the position of the shaft in the housing. The motor is used to rotate the shaft and, hence, the tool. For example, a tool such as a machining bit can be connected to the shaft, and the spindle can be used in a high speed machining device such as a computer numerical control (CNC) machine device for machining structural materials. Alternatively, a spindle can be used in conjunction with an external rotational device, such as a motor, and with no motor provided within the housing. Thus, the spindle can comprise a shaft that is mounted in a housing, for example, with bearings or bushings to support the shaft so that the shaft is freely rotatable.
Each device and process that uses a spindle requires the spindle to have particular characteristics such as size, strength, maximum torque, fatigue resistance, and the like. If a spindle is not properly matched with the device and process for which it is used, the spindle can wear excessively and fail prematurely. For example, the spindle described above for use in a high speed machining device can fail if the spindle motor overheats, the shaft breaks, bearings or bushings wear or heat excessively, and so forth. Failure of a spindle can require repair or replacement, adding to the cost of the operation of the device. Additionally, a failed spindle can interrupt the operation of the device, thereby incurring costs associated with machine downtime such as delays in production, loss in productivity, and wasted materials.
Past attempts have been made to evaluate the effectiveness of a spindle before the spindle is used in a particular application. For example, if a spindle is to be used in a CNC machine device for machining aluminum parts, the spindle can be subjected to a test to determine the effectiveness of the spindle in such an application. In particular, the spindle can be installed in a test device that is similar to the machine in which the spindle is to be used, so that the test device applies stress to the spindle similar to that which would occur during operation. The test device can be operated continuously until the spindle fails. Thus, the test can be used to determine an expected longevity of the spindle in the application, and the temperature and vibration characteristics of the spindle can also be measured during the test period. However, such a test requires time and personnel for conducting the test. Further, the aluminum or other material that is machined or otherwise consumed during testing can be costly.
Alternatively, the test device can include a dynamometer that is mechanically coupled to the spindle. The dynamometer can be used to exert a particular rotational resistance on the spindle over a test period to determine the power and torque output of the spindle during the test period. Testing with a dynamometer can save the expense of wasted material that is consumed, but the dynamometer adds to the cost of the test device. Moreover, the dynamometer does not measure or test other factors that influence the effectiveness of the spindle. For example, a spindle can be subject to side or axial loads during typical operation that are not applied during testing. Such loading can substantially decrease the operating life and effectiveness of the spindle. Additionally, in typical operation, the spindle may be subjected to vibrations or other cyclical forces, for example, in phase with the impact of teeth or blades of the tool on the workpiece. These vibrations or other cyclical forces, which are not applied or measured by the dynamometer during testing, can substantially affect the operation and life of the spindle, thereby reducing the accuracy of the test.
Thus, there exists a need for an improved apparatus and method for testing spindles. The apparatus should be capable of testing various types of spindles by subjecting each spindle to particular torques, axial loads, side loads, and cyclical forces, continuously or according to a predetermined schedule. The apparatus should also be compatible with monitoring equipment to determine the effectiveness of the apparatus under predetermined conditions.